1. Field of the Invention
The invention concerns the use of fatty alcohol polyglycolethers with closed end-groups as foam-depressing additives in low-foam, sprayable cleaning agents.
2. Discussion of Related Art
Aqueous cleaning agents intended for use in commerce and industry, in particular those for cleaning metallic, glass, ceramic and plastic surfaces, generally contain substances which are capable of counteracting the unwanted formation of foam. The use of foam-depressing additives is required in the majority of cases because the impurities which are loosened from the substrates and which collect in the cleaning baths act as foaming agents. In addition, the use of anti-foaming agents may also be necessary because the cleaning agents themselves contain constituents which give rise to the unwanted formation of foam under the prescribed operating conditions, e.g., anionic surfactant or nonionic surfactant which foams at the operating temperature.
Thus, e.g. in the industrial cleaning process in the metal industry, good wetting alkaline aqueous solutions are used as cleaning agents to remove drawing and rolling oils or grease and organic corrosion inhibitors containing carboxyl groups. These solutions must be sprayable and free from foam at a pressure of 3 to 30 bar and a temperature of 20.degree. to 90.degree. C. For this reason, these cleaning operations require surfactants which not only produce little foam themselves, but which simultaneously act as defoamers for the other surfactant components used with them, e.g. anionic surfactants such as the surfactants containing alkylbenzene sulfonates or other sulfonic acid groups and carboxyl groups.
These desired properties are found, for example, in a class of nonionic surfactants which are generally known as ethylene oxide-propylene oxide block copolymers and are described e.g. in U.S. Pat. No. 2,674,619. These are particularly higher molecular weight compounds with a polyether structure which have marked foam-depressing properties and at the same time good dispersibility. However, these nonionic surfactants which are specifically geared to industrial cleaning processes have the serious disadvantage that they are not sufficiently biologically degradable according to the testing procedures for the surface-active compounds under the German Detergents Act.
German patent application No. 33 15 951 describes the use of polyethyleneglycolethers of the general formula Ia EQU R.sup.1 --O--(CH.sub.2 CH.sub.2 O).sub.n --R.sup.2 (Ia)
in which R.sup.1 represents a straight-chain or branched alkyl radical or alkenyl radical with 8-18 C atoms, R.sup.2 represents an alkyl radical with 4-8 C atoms and n a number from 7 to 12, as foam-depressing additives in cleaning agents. These compounds, however, show no anti-foaming effect below 20.degree.-25.degree. C. It is, however, the foam-inhibition at low temperatures that is desired.
The problem at the basis of the present invention was therefore to find foam-depressing substances with industrial application properties which are superior to those of the agent in the prior art at temperatures below 20.degree.-25.degree. C. and which at the same time have the necessary biological degradability. The solution to this problem came from the realization that certain short-chain end-group closed addition products of ethylene oxide on selected aliphatic alcohols defined in the following can meet the set requirements both with regard to their usability for industrial applications (foam inhibition and stable formulation in the temperature range of -5.degree. to +50.degree. C.) and their biological degradability.
It is therefore an object of this invention to provide a nonionic surfactant which meets the desired requirements in particular for industrial cleaning processes.